Disease control ranks at No. 4 in Keys to Peanut Profitability

• Great strides have been made in peanut disease control in recent years, especially through the development of genetically improved varieties. But as producers look ahead to the 2012 production season, white mold looms large as a serious disease threat.

Organizers of the Farm Press Peanut Profitability Award have reviewed production data from previous winners to arrive at a “Top 10 Keys to Peanut Profitability.” This list of successful production practices is being presented in descending order in Southeast Farm Press and on this website, with sponsorship provided by DuPont Crop Protection. The Peanut Profitability Awards, based on production efficiency in whole-farm situations, is entering its 13th year and is administered by Marshall Lamb, research director for the National Peanut Research Laboratory, and his staff.

As the countdown continues to the No. 1 Key to Peanut Profitability, disease control comes in at No. 4, including the control of soil-borne and foliar diseases and nematodes.

Great strides have been made in peanut disease control in recent years, especially through the development of genetically improved varieties. But as producers look ahead to the 2012 production season, white mold looms large as a serious disease threat.

White mold has become one of the most important, if the not the most important disease faced by Georgia peanut producers, according to Bob Kemarit, University of Georgia Extension plant pathologist.

“No matter what you call it — white mold, stem rot, Southern stem blight — the bottom line is that every grower has to fight white mold, to a greater or lesser degree.

“No grower will control white mold 100 percent, no matter what you do. In the best situation in a bad year, getting 60 to 70 percent control might be the best you can do, and that’s with your best fungicides and your best efforts,” says Kemerait.

White mold is an important disease, he adds, and resistant varieties are rare, although Georgia-07W is one good example.

“Fungicides add to production costs, but it’s a good investment,” says Kemerait.

“As tomato spotted wilt has diminished, our losses to white mold on a regional basis are much greater than to any other disease in peanuts. You can argue that controlling peanut leaf spot adds significant cost to a production program.

“But when you look at the yield loss associated with white mold, despite a fungicide program, regionally it’s much greater than for any other disease.”

Peanuts are a susceptible host to white mold. Also, hotter temperatures like those experienced by producers in the lower Southeast also encourage the development of the disease.

White mold is special case

White mold is a “special case” for peanut producers compared to other soil-borne diseases, says Kemerait.

“Maybe one-third of growers have seen CBR in their fields. Both CBR and white mold are serious diseases, and both cost growers in terms of a significant amount of worry, and of lost yields. Also, the symptoms of the two diseases can appear very similar.”

The diseases are spread by sclerotia or fungal “seeds”, he says. They both survive in the soil, waiting for the next peanut crop.

“Sclerotia attack the part of the plant that is closest to the soil. They’re called soil-borne because their survival structure and fungus are growing in the soil.”

It’s important, he says, that growers understand how CBR and white mold are different from one another.

“While environment is important with white mold, it’s even more important with CBR. If we have hot, dry conditions or a hot spring, we won’t get much CBR.

“It is driven by cooler temperatures. Early infection by the CBR pathogen occurs on the developing root system. White mold likes warmer temperatures. Even if it’s cool during the first part of the season, white mold will jump up later in the year. White mold needs oxygen, and it can be the biggest problem around the crown of the plant.

“While both CBR and white mold are severe on a field-by-field basis, I would rather have a bad case of white mold any year than a bad case of CBR. CBR survives longer in the soil. Also, managing CBR is much more difficult and the yield losses can be as bad, or worse, than white mold. On a field-by-field basis, I believe CBR is worse than white mold.”

However, every grower has to fight white mold, says Kemerait. The disease is found over a much greater part of the world, and it’s found over a greater part of the Southeast.

“If you have soybeans, you may have white mold, and it’ll even go to vegetables. So the distribution is larger than with CBR.”

Environment also is a big factor, says Kemerait. “We will always have conditions at some time of the year that will be favorable for white mold outbreaks. It’s not a matter of if you’re going to have it, but when you’re going to have it. Hot temperatures earlier mean an earlier epidemic, but it’s going to eventually get hot in the South.”

CBR infects a limited number of plants, including soybeans, coffeeweeds and peanuts. White mold, on the other hand is found on 180 to 200 species of plants. Because of this, white mold is likely to affect your location in one way or another, he says.

Control begins with rotation

“The best way to reduce the inoculum buildup of white mold is to rotate away from peanuts and soybeans and other susceptible crops and deep turn the soil. Sclerotia (fungal “seeds”) of the white mold fungus will survive for several years in the top inch of soil where oxygen is plentiful. If you bury the sclerotia, they survive for about one year.”

It’s also important, says Kemerait, to choose an appropriate fungicide program for controlling white mold.

“Every grower will consider using tebuconazole this year. It’s cheap, and it’s a good fungicide. But don’t use it just because it’s cheap — make your fungicide choice based on the pressure in your field and your needs. The newer fungicides coming out have efficacy towards white mold that surpasses what you’d normally expect from tebucoanzole.”

“Initiating a white mold program at 60 days after planting has been our general recommendation for years. But knowing that white mold can come in earlier in a warm year, and you know you have the option of cheap applications of tebuconazole, you might consider starting your fungicide program a little early, while keeping your standard program white mold program intact later in the season.

“Another option might be to simply start your standard program earlier than normal, for example 45-50 days after planting and then extending it with additional applications of an appropriate fungicide.”

Research also has shown the benefits of applying fungicides at night or early in the morning. The biggest challenge of managing white mold is getting the fungicide to the target, says Kemerait, and by spraying at night, you have a clear path to the target.

“Spraying at night allows us to get the fungicide where we need it, and we don’t have to deal with a heavy canopy.

“We recommend irrigating after applying a fungicide or spraying ahead of a rain event because we need some vehicle to move the fungicide down.

“Spraying at night gets it to where it needs to be. It improves your white mold control in a bad situation.”

In 1994, the game changed for peanut white mold control, he says, with the introduction of Folicur. It was followed in 1995 by Abound. Now, there are several options in terms of fungicides for controlling the disease.

“We get the best performance from these fungicides through rotation, selecting a resistant variety, and, regardless of the fungicide program you choose, making sure you stay on time and ahead of disease.”

New fungicides are available, says Kemerait, including Fontelis from DuPont that received registration this year and has shown excellent control of white mold.

Research has shown, he says, that the impact of a white mold control program can begin two to three weeks after the plant comes up.

“Sixty days has been the historical timing to begin a soilborne fungicide program, but early season fungicide applications can be very important.

“We can do this by banding a full 5.7-ounce broadcast rate of Proline from Bayer Cropscience over the row at early emergence. Early emergence refers to a fungicide application between two and five weeks after planting. Timing of applications and the fungicide you choose go a long way in managing white mold.”

(To see the introduction to this countdown to peanut profitability, click here. To read about No. 10 and No. 9, click here. Keys No. 8 and No. 7 can be found by clicking here. No. 6 and No. 5 can be found here).